Laboratory animal allergy (LAA) affects up to 20% of laboratory animal workers and a significant proportion go on to develop occupational asthma (OA). Exposure is an important risk factor for LAA and OA, but it is logistically difficult to perform regular exposure assessments on a large group of workers. A mouse allergen monitoring program has been established at The Jackson Laboratory, and preliminary cross sectional data suggest that serum levels of mouse allergen-specific IgG and IgG4 increase with cumulative mouse allergen exposure and that mouse-specific IgG and IgG4 may be predictive of the development of mouse-specific IgE. Mouse-specific IgG and IgG4, then, may prove to be an appropriate biomarker for monitoring exposure over time among mouse workers and for ultimately predicting risk of allergic sensitization. However, before a long-term, comprehensive prospective cohort study can be undertaken to determine the value of mouse-specific IgG and IgG4 in predicting risk of allergic sensitization, the feasibility of such a study needs to be determined. The two goals of this proposal, which will prepare for that prospective study, are to evaluate and compare two methods of measuring allergen exposure, room monitoring and personal monitoring, and to examine the relationship between mouse-specific IgG and IgG4 and cumulative allergen exposure testing the hypothesis that these IgGs can serve as biomarkers of exposure.